Control Entity and Method for Setting up a Session in a Communications Network, Subscriber Database and Communications Network

ABSTRACT

Control entity and method for setting up a session in a communications network, subscriber database and communications network The invention relates to a control entity for setting up a session in a communications network, comprising an input device for receiving a request to set up a session in the communications network, a processor unit for processing the request, and an output device for sending messages. The control entity further comprising or having access to a memory for storing information. The processor unit is arranged to determine if the request comprises a valid Communication Service Identifier, CSI, the Communication Service Identifier identifying the type of communication service of the session that is to be established over the communications network. And if the request does not comprise a valid Communication Service Identifier to execute a default CSI procedure using default CSI information stored in the memory.

TECHNICAL FIELD

The invention relates to a control entity, such as a Call/SessionControl Function (CSCF) for an IP Multimedia Subsystem (IMS) network(Proxy CSCF (P-CSCF) or Serving CSCF (S-CSCF)). The invention furtherrelates to a method for setting up a session in a communicationsnetwork, such as an IMS network, subscriber database, such as a homesubscriber server (HSS), arranged to be part of a communicationsnetwork, method for registering a user terminal (UE—user equipment) in acommunications network, communications network, computer program and adata carrier.

BACKGROUND

IP Multimedia Subsystem (IMS) is the technology defined by the ThirdGeneration Partnership Project (3GPP) to provide IP Multimedia servicesover mobile communications networks (3GPP TS 22.228). IMS provides keyfeatures to enrich the end-user person-to-person communicationexperience through the integration and interaction of services. IMSallows new rich person-to-person (client-to-client) as well asperson-to-content (client-to-server) communications over an IP-basednetwork.

The IMS makes use of the Session Initiation Protocol (SIP) to set up andcontrol calls or sessions between user terminals (UEs) or between UEsand application servers (AS). The Session Description Protocol (SDP),carried by SIP signalling, is used to describe and negotiate the mediacomponents of the session. Whilst SIP was created as a user-to-userprotocol, IMS allows operators and service providers to control useraccess to services and to charge users accordingly.

Within an IMS network, control entities, which set up and control callsor sessions, such as Call/Session Control Functions (CSCFs) operate asSIP entities within the IMS. The 3GPP architecture defines three typesof CSCFs:

the Proxy CSCF (P-CSCF) which is the first point of contact within theIMS for a user terminal UE (also referred to as SIP terminal);

the Serving CSCF (S-CSCF) which provides services to the user that theuser is subscribed to; and

the Interrogating CSCF (I-CSCF) whose role is to select the correctS-CSCF during registration and, in a terminating session, to find thecorrect S-CSCF that serves the targeted user terminal.

IMS application services are implemented using application servers (AS).For any given public user identity, one or more application servers maybe linked in by the S-CSCF on communication originated or terminated tothat users UE. Application servers communicate with an S-CSCF via theIMS Service Control (ISC) interface and are linked into a SIP messagingroute as required (e.g. as a result of the triggering of Initial FilterCriteria (IFC) downloaded into the S-CSCF for a given UE).

A user terminal UE registers in the IMS network using the specified SIPREGISTER method. This is a mechanism for attaching to the IMS networkand announcing to the IMS network the network address at which a SIPuser identity can be reached. In 3GPP, when a SIP terminal performs aregistration, the IMS network authenticates the user using subscriptioninformation stored in a Home Subscriber Server (HSS), and allocates anS-CSCF to that user from the set of available S-CSCFs. Whilst thecriteria for allocating S-CSCFs are not specified by 3GPP, these mayinclude load sharing and service requirements. It is noted that theallocation of an S-CSCF is key to controlling, and charging for, useraccess to IMS-based services. Operators may provide a mechanism forpreventing direct user-to-user SIP sessions which would otherwise bypassthe S-CSCF.

During the registration process, it is the responsibility of the I-CSCFto select an S-CSCF, if an S-CSCF is not already selected. The I-CSCFreceives the required S-CSCF capabilities from the HSS, and selects anappropriate S-CSCF based on the received capabilities. It is noted thatS-CSCF allocation is also carried out for a user by the I-CSCF in thecase where the user is called by another party, and the user is notcurrently allocated an S-CSCF. When a registered user subsequently sendsa session request to the IMS network, the P-CSCF is able to forward therequest to the selected S-CSCF based on information received from theS-CSCF during the registration process.

3GPP has defined the IMS Communication Service Identifier (ICSI) toexplicitly identify the type of communication service that is to beestablished over the IMS network. The ICSI may be incorporated in arequest initiating a session. The IMS network elements and theterminating user terminal UE need to have the same understanding of whatcommunication service is requested. One example is to separate the twoincompatible IMS implemented “voice” services from each other, PoC(Push-to-talk) and Multimedia telephony. The ICSI is used also for manyother purposes such as:

-   -   Linking in Application Servers over IMS Service Control (ISC),    -   Discrimination in end-points to the correct software module,    -   Policy handling and enforcement, and    -   Interconnect between operators.

The IMS Communication Service Identifier (ICSI) has been included in3GPP.

A problem may occur when a user terminal UE connects to an IMS networkwithout including an ICSI which may lead to several nodes having to“guess” what communication service to execute their service logic for.

As described above, the reason why a user terminal UE may not include anICSI may e.g. be that the user terminal UE is a legacy terminal thatdoes not support the IMS Communication Service Identifier. However, itis also possible that the user terminal UE generates an IMSCommunication Service Identifier that does not conform to any of thecommunication services defined in the IMS network and is not recognizedby the IMS network. For both examples there is no appropriate way ofdealing with such requests.

It is an object to enable processing of requests for sessions that donot properly specify the kind of service that is requested.

SUMMARY

This object is achieved by the methods as described in claim 11 and 23.Furthermore, the invention is embodied in a control entity according toclaim 1 and a subscriber database according to claim 20, an IPMultimedia Subsystem network according to claim 25, computer programsaccording to claim 27 and a data carrier according to claim 28.Advantageous embodiments are described in the further claims.

According to an aspect there is provided a Control Entity for setting upa session in a communications network. The control entity comprises aninput device for receiving a request to set up a session in thecommunications network, a processor unit for processing the request, andan output device for sending messages.

The control entity further comprises or has access to a memory forstoring information. The processor unit is arranged to determine if therequest comprises a valid Communication Service Identifier (CSI). TheCommunication Service Identifier identifies the type of communicationservice of the session that is to be established over the communicationsnetwork. If the request does not comprise a valid Communication ServiceIdentifier the processor unit is arranged to execute a default CSIprocedure using default CSI information stored in the memory. Hence, theinvention allows that for a request to set up a session in thecommunications network, a proper identification of the type ofcommunication service that is required for the request is available. Thecontrol entity, such as a P-CSCF or a S-CSCF, is enabled to identify thetype of communication service required, even if the CSI as received inthe request is not valid, e.g. is missing, not supported or notrecognized. Subsequently the control entity can process the requestaccordingly.

According to an embodiment there is provided a control entity, whereinin case the request does not comprise a Communication Service Identifierthe default CSI procedure comprises adding a default CSI to the request,where the default CSI is specified by the default CSI information.

According to an embodiment the default CSI procedure comprises testingat least one parameter in the request and deciding based on the at leastone tested parameter and the default CSI information to add a defaultCSI to the request, where the default CSI is specified by the defaultCSI information, or not to add a default CSI to the request.

According to an embodiment the at least one parameter may be acombination of the type of request and the type of media. In case thecommunications network is an IP Multimedia Subsystem network, the typeof request may be one of INVITE request, MESSAGE request, REFERrequests, SUBSCRIBE request, and the type of media may be one of audio,video.

According to an embodiment, in case the request comprises aCommunication Service Identifier that is not recognized or supported bythe control entity or the communications network, the default CSIprocedure decides to allow or abort the request based on the default CSIinformation.

According to an embodiment the control entity is a Proxy Call SessionControl Function that is arranged to act as a first point of contactwithin the communications network for a user terminal, and is arrangedto receive a request from a user terminal for setting up a session inthe communications network with a remote user terminal.

According to an embodiment the default CSI information is specific forthe user terminal the request is received from.

According to an embodiment the control entity is a Serving Call SessionControl Function that in use is arranged to provide services, and isarranged to receive a request from an application server for setting upa session in the communications network.

According to an embodiment the default CSI information is specific forthe user terminal on behalf of which the request is made by theapplication server.

According to an embodiment the control entity is a Proxy Call SessionControl Function and a Serving Call Session Control Function.

According to an aspect there is provided a method for setting up asession in a communications network, wherein a control entity performsthe steps of receiving a request for setting up a session in thecommunications network, determining if the request comprises a validCommunication Service Identifier (CSI), the Communication ServiceIdentifier identifying the type of communication service of the sessionthat is to be established over the communications network. And if therequest does not comprise a valid Communication Service Identifier, themethod further comprises executing a default CSI procedure using defaultCSI information.

According to an embodiment in case the request does not comprise aCommunication Service Identifier the default CSI procedure comprisesadding a default CSI to the request, where the default CSI is specifiedby the default CSI information.

According to an embodiment the default CSI procedure comprises testingat least one parameter in the request and deciding based on the at leastone tested parameter and the default CSI information to add a defaultCSI to the request, where the default CSI is specified by the defaultCSI information, or not to add a default CSI to the request.

According to an embodiment the at least one parameter may be acombination of the type of request and the type of media. In case thecommunications network is an IP Multimedia Subsystem network the type ofrequest may be one of INVITE request, MESSAGE request, REFER requests,SUBSCRIBE request, and the type of media may be one of audio, video.

According to an embodiment there is provided a method as described,where in case the request comprises an Communication Service Identifierthat is not recognized or supported by the control entity or thecommunications network, the default CSI procedure decides to allow orabort the request based on the default CSI information.

According to an embodiment the request is a request from a user terminalfor setting up a session in the communications network with a remoteuser terminal.

According to an embodiment the default CSI information is specific forthe user terminal the request is received from.

According to an embodiment the request is a request from an applicationserver for setting up a session in the communications network.

According to an embodiment the default CSI information is specific forthe user terminal on behalf of which the request is made by theapplication server.

According to an aspect there is provided a subscriber database arrangedto be part of a communications network. The subscriber databasecomprises an input device for receiving a register message from a userterminal, a processor unit for processing the register message, and anoutput device. The subscriber database further comprises or has accessto a memory for storing subscription information. The subscriberdatabase is arranged to generate default CSI information based uponsubscription information stored in the memory in reaction to the receiptof the register message, and to transmit the generated default CSIinformation to at least one control entity in the communications networkvia the output device. This allows that when a user terminal registersin the communications network, default CSI information is made availablefor the user terminal. This default CSI information can be used bycontrol entities, e.g. P-CSCF or S-CSCF, for properly handling requestsfor set up of sessions, including identifying the appropriatecommunication services.

According to an embodiment the default CSI information is specific forthe user terminal the register message is received from.

According to an embodiment the subscriber database is arranged to workin an IP Multimedia Subsystem network, and the subscriber database is ahome subscriber server.

According to an aspect there is provided a method for registering a userterminal in a communications network, wherein a subscriber databaseperforms the steps of receiving a register message from a user terminal,generating default CSI information based upon subscription informationin reaction to the receipt of the register message, and transmitting thegenerated default CSI information to at least one control entity in thecommunications network.

According to an embodiment the default CSI information is specific forthe user terminal the register message is received from.

According to an aspect there is provided an IP Multimedia Subsystemnetwork, comprising at least one control entity as described and atleast one subscriber database as described.

According to an embodiment the at least one control entity is at leastone Proxy Call Session Control Function as described and at least oneServing Call Session Control Function as described.

According to an aspect there is provided a computer program, when loadedon a computer, provides the computer with the functionality to performone of the methods described.

According to an aspect there is provided a data carrier, comprising acomputer program as described.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying schematic drawings in which correspondingreference symbols indicate corresponding parts, and in which:

FIG. 1 schematically depicts an IMS network,

FIG. 2 a schematically depicts a computer,

FIG. 2 b schematically depicts a control entity such as a P-CSCF orS-CSCF according to an embodiment,

FIGS. 3 and 4 schematically depict a flow diagram according to anembodiment, and

FIGS. 5, 6 and 7 schematically depict a sequence diagram according toembodiments, and

FIG. 8 depicts a flow diagram according to a control entity according toan embodiment.

DETAILED DESCRIPTION

In the following it will be described how the invention may beimplemented in an IMS network. It is apparent to a person skilled in theart that the IMS network is only an example of a communications networkwhere the invention could apply, the invention may also be implementedin other communications networks, like a GSM, Code Division MultipleAccess (CDMA), Time Division Multiple Access (TDMA), Universal MobileTelecommunication System (UMTS), or 4G network.

IMS Network

FIG. 1 schematically depicts the main components of an IMS network. FIG.1 shows a user terminal UE (also referred to as IMS terminals) that isarranged to set up a session or a call with each other. Such a userterminal UE is arranged to connect to an IMS network by using thestandard Internet Protocol (IP). User terminals UE may for instance be amobile telephone, a PDA, a computer.

The main components of the IMS network shown in FIG. 1 are, as alreadymentioned above, Call/Session Control Functions (CSCFs) that operate asSIP entities within the IMS network, to control the sessions within theIMS network.

Three types of CSCFs are provided:

-   -   the Proxy CSCF (P-CSCF) which is the first point of contact        within the IMS for a SIP terminal;    -   the Serving CSCF (S-CSCF) which provides services to the user        that the user is subscribed to; and    -   the Interrogating CSCF (I-CSCF) whose role is to select the        correct S-CSCF during registration and, in a terminating        session, to find the correct S-CSCF that serves the targeted        user terminal.

Furthermore, FIG. 1 comprises an application server AS which interactswith the S-CSCF. The application server (AS) provides services to userterminal UE, such as multimedia telephony services, push-to-talkservices, messaging services, Voice Call Continuity (VCC) services, etc.These services can be further detailed, with originating/terminatingcall barring, originating/terminating call screening, call diversionservices, calling line presentation services, as examples of servicesprovided for multimedia telephony. It will be understood that moreapplication servers AS may be provided.

The application server AS may also initiate sessions it self, forinstance for initiating a Wake up service, Click to talk (Call setup viapushing a phone item on a website, the web portal interacting with anapplication server capable of setting up a session) or an automatedretry. A session that is set up by the application server AS uses theS-CSCF, but does not use an originating P-SCSF. This will be referred toas application server initiated originated SIP communication.

FIG. 1 further shows a Home Subscriber Server HSS, which in fact is adatabase comprising information about the IMS network. The HSS maycomprise information about the user's subscription, i.e. user profiles.Also, the HSS plays an important role when a user terminal registers tothe IMS network, as it authenticates and authorizes the user terminalUE. HSS comprises information about the location of a user (allocatedS-CSCF) and provides information to an S-CSCF that is used as part ofthe registration procedure, e.g. by providing the S-CSCF withauthentication parameters (which authentication method to be used anddata for performing the chosen authentication method). HSS alsodownloads the user profile to the S-CSCF that e.g. contains the InitialFilter Criteria instructing the S-CSCF which application servers AS thatshall be linked in over the ISC interface for originating andterminating SIP transactions.

As described above, the P-CSCF is the first point of contact for theuser terminal UE. So, all messages that come from or go to the userterminal UE travel through the P-CSCF. At registration, a P-CSCF isassigned to the user terminal UE. The assigned P-CSCF remains the samefor a user terminal UE until a new registration is made.

The S-CSCF is located in the home network and makes contact with thecalled subscriber's network to establish a session between the two userterminals UEs. The called user terminal UE may belong to the same IMSnetwork as the calling user or belong to an outside IMS network or evenan outside network of another type, such as PSTN/PLMN. In latter case,the call is routed to PSTN/ISDN via the BGCF (Border Gateway ControlFunction) and MGCF (Media Gateway Control Function) functional entities.

The I-CSCF is located near the border of the part of the IMS networkbelonging to a certain provider. I-CSCF's have an IP-address that isknown (or retrievable) to other I-CSCF's such that I-CSCF's can findeach other and exchange SIP packets. The I-CSCF use information from theHSS to locate the S-CSCF serving the user terminal UE within its domainand forward a SIP message received from a remote IMS network to thatS-CSCF.

FIG. 1 is divided in two parts by a vertical dashed line. The left handside has been described above. However, the right hand side of FIG. 1forms a mirror image of the left hand side and comprises similar devicesand nodes as the left hand side: a user terminal UE2, a the Proxy CSCF(P-CSCF2), a Serving CSCF (S-CSCF2), an Interrogating CSCF (I-CSCF2), anapplication server AS2 and a Home Subscriber Server HSS2.

Both the left hand side and the right hand side form part of the IMSnetwork belonging to a certain provider and the dashed line indicatesthe border of the part of the IMS network belonging to a certainprovider. Below, the explanation and embodiments focus on one side only,but of course it will be understood that the embodiments may be put topractice in the total IMS network.

It will be understood that an IMS network may comprise more and othernodes than shown in FIG. 1. Nodes may also be present more than once,for instance for load balancing or organizational reasons. Also, nodesthat are shown as separate nodes may in fact be formed as one element,incorporating the functions of the incorporated nodes. Also, nodes maybe split in two or more nodes.

General Computer

In fact, all elements shown in FIG. 1 may be formed as a computer. FIG.2 a schematically shows a general embodiment of an example of acomputer. The description may refer to several kind of devices, such aspersonal computers, servers, laptops, personal digital assistances(PDA), palmtops, telephones. All these devices are different kind ofcomputers.

FIG. 2 a shows a schematic block diagram of an embodiment of a computer10, comprising a processor unit PU for performing arithmeticaloperations. The processor unit PU is connected to memory ME that maystore instructions and data. The memory ME may be formed by one or moreof a tape unit, hard disk, a Read Only Memory (ROM), ElectricallyErasable Programmable Read Only Memory (EEPROM), a Random Access Memory(RAM). The memory may comprise instructions that are readable andexecutable by the processor unit PU to enable the computer 10 to performthe embodiments described.

The processor unit PU may also be connected to one or more inputdevices, such as a keyboard KE, and one or more output devices, such asa display DI, and one or more reading units RU to read for instance afloppy, CD ROM's CR, a DVD.

The computer 10 shown in FIG. 2 a also comprises an input output device(I/O) that is arranged to communicate with other computers (not shown)via a network, for instance the IMS network. Of course, the input outputdevice (I/O) may also be formed as a separate input device I and outputdevice O.

However, it should be understood that there may be provided more and/orother memory units, input devices and read devices known to personsskilled in the art. Moreover, one or more of them may be physicallylocated remote from the processor unit PU, if required. The processorunit PU is shown as one box, however, it may comprise several processingunits functioning in parallel or controlled by one main processor unitthat may be located remote from one another, as is known to personsskilled in the art.

It is observed that, although all connections in FIG. 1 are shown asphysical connections, one or more of these connections can be madewireless. They are only intended to show that “connected” units arearranged to communicate with one another in someway.

The computer 10 is shown as a computer, but can be any signal processingsystem with analog and/or digital and/or software technology arranged toperform the functions discussed here.

FIG. 2 b shows a control entity CE, such as a P-CSCF and a S-CSCF in amore schematic way. The control entity CE comprises the processor unitPU, arranged to communicate with the memory ME. The control entity CEfurther comprises an input device I and an output device O (possiblyintegrated in one input output device I/O) for receiving andtransmitting respectively.

FIG. 2 c shows a subscriber database SD, such as a Home SubscriberServer (HSS) in a more schematic way. The subscriber database SDcomprises the processor unit PU, arranged to communicate with the memoryME. The subscriber database SD further comprises an input device I andan output device O (possibly integrated in one input output device I/O)for receiving and transmitting respectively.

Registering/Inviting

In order to be registered in the network, user terminals UE may send aREGISTER message to the IMS network, the REGISTER message being providedaccording to the SIP-protocol. As described above, when a user terminalUE registers in the IMS network, the specified SIP REGISTER proceduremay be used. As a result of the SIP REGISTER procedure, the networkaddress at which the user terminal UE can be reached is known to theS-CSCF selected to serve that user, and the allocated S-CSCF will beknown at the HSS. Also, a S-CSCF and a P-CSCF are assigned to the userterminal UE as part of the Registration procedure.

After registration has taken place the user terminal UE may send anINITIAL REQUEST message to the IMS network to open a session with aremote user terminal UE, the INITIAL REQUEST message being providedaccording to the SIP-protocol. The INITIAL REQUEST message may triggerthe IMS network to set up a session with a certain remote end user UE.

The INITIAL REQUEST may be any kind of request or in particular a SIPrequest message, including INVITE request, MESSAGE request, REFERrequests, SUBSCRIBE request, etc., as will be understood by a skilledperson. The term INITIAL REQUEST as used here refers to all suchrequests. In fact, an INITIAL REQUEST does not necessarily be the firstmessage that is exchanged between the user terminal UE and the IMSnetwork.

As described above, user terminals UE may use the IMS network fordifferent kind of services, such as initiating a peer to peercommunication session or a multi media conference session or a messagingsession. In order to indicate what kind of service is requested, theINITIAL REQUEST message may comprise an ICSI.

The ICSI provided by the user terminal UE at the beginning of sessionsetup identifies a particular communication service provided by the IMSnetwork. It allows that for a particular communication service thecorrect application logic can be invoked in the terminals and in thecorrect application servers (AS's) to be linked in over the ISCinterface. This ensures that requests do not have to travel through anumber of not applicable AS's before the correct application logic canbe executed. This also ensures efficient handling of differentcommunication services provided by the IMS network.

Furthermore it allows different bearer/media/qos policies to be enforcedfor the different communication services.

ICSIs may be used to:

-   -   decide which media authorization policies to apply    -   decide which communication service authorization policies to        apply    -   decide which priority to assign in overload situations    -   decide which interworking to apply    -   decide which is the correct terminating device to route to    -   decide which charging policies to apply    -   decide which application to invoke on the terminating device    -   to communicate the kind of communication services a UE is        capable to provide (presence)    -   decide which application server to invoke    -   decide which interoperator service agreements to apply

Some user terminals UE will be arranged to include an ICSI in theirINITIAL REQUEST, indicating which service is requested. Other userterminals UE may not be arranged to include an ICSI, making it difficultfor the IMS network to know what kind of service is requested by theuser terminal UE. As a result, the IMS network will have to guess whatkind of service is requested and may perform a “best attempt” toidentify the requested service.

Based on the above it will be understood that the information about therequested service needs to be known at different nodes in the IMSnetwork. Without an explicit means to identify what service isrequested, each node that needs to know this is required to make aguess. The S-CSCF may try to identify the application server AS to linkin based upon very complicated iFCs. iFC means Initial Filter Criteria,which is a component of the subscription data downloaded to the S-CSCFat server assignment during registration. It tells the S-CSCF on whatconditions an AS shall be linked in over the ISC interface. The P-CSCFmay have to make a guess in order to understand the correct way toproceed.

If no ICSI is provided, it is not ensured that all the nodes in the pathof the request will all correctly identify the requested service. Also,when an ICSI is provided that is not supported by the user terminal UEthat does not conform to any of the communication services defined inthe IMS network, a similar problem arises.

Embodiments

According to the embodiments it is proposed to centralize a“default-ICSI” decision, and to have the enforcement of this decisiondivided on two nodes, depending on which traffic case to execute. It isproposed to provide a mechanism to instruct a P-CSCF how to handle anINITIAL REQUEST not comprising an ICSI or comprising an ICSI that is notsupported or recognised by the IMS network.

It is further proposed to provide a mechanism to instruct the S-CSCF howto handle an INITIAL REQUEST not comprising an ICSI or comprising anICSI that is not supported or recognised by the IMS network, both forINITIAL REQUESTS originating from a user terminal UE or an applicationserver AS.

Both mechanisms may comprise the option of adding a default ICSI to theINITIAL REQUEST if the INITIAL REQUEST does not comprise an ICSI, or todecide if an INITIAL REQUEST comprising an ICSI that is not recognizedor supported is to be allowed or not.

The default ICSI information is used by a default ICSI procedure fordetermining the default communication service to use for a particularcall initiation and subscriber.

Registration

According to an embodiment, it is proposed to extend the registrationprocedure as described above, including setting default ICSI informationin the IMS network. As part of the registration procedure of aparticular user terminal UE, default ICSI information about thisparticular user terminal UE is provided to specific nodes in the IMSnetwork.

A user terminal UE may register in the normal fashion and theregistration procedure is herein proposed to be extended with providingdefault ICSI information to the P-CSCF, to enable the P-CSCF todetermine what to do when an INITIAL REQUEST is received that does notcomprise an ICSI or comprises an ICSI that is not supported orrecognised by the IMS network. The default ICSI information will beprovided or made accessible to the IMS network by the HSS.

Furthermore, the registration procedure is herein proposed to beextended with providing default ICSI information to the S-CSCF, toenable the S-CSCF to determine what to do when an application serverinitiates originated SIP communication that does not comprise an ICSI orcomprises an ICSI that is not supported or recognised by the IMS networkis received.

The proposed embodiments can be used for any SIP communication in a newSIP session. The P-SCSF or the S-CSCF are arranged to execute thedefault ICSI procedure using the default ICSI information relevant forthe respective user terminal UE. The default ICSI information isprovided or made accessible to the P-SCSF and/or S-CSCF during theregistration.

The content of the default ICSI information can be different fordifferent user terminals UE providing a relatively flexible IMS network.The content of the default ICSI information may for instance depend onspecific subscription information of the user terminal UE, which isknown in the HSS.

Default ICSI Procedure

Upon successful registration default ICSI information is provided to theP-CSCF and/or the S-CSCF, based on which the P-CSCF and/or S-CSCF mayexecute the default ICSI procedure to decide how to process an INITIALREQUEST not comprising a valid ICSI. The default ICSI information isspecific for the registered user terminal UE. Four options can beidentified:

1) No default ICSI is enforced; this means that no ICSI is added to theINITIAL REQUEST message on calls originated through it.

2) A default ICSI is enforced; this means that a default ICSI is addedto the INITIAL REQUEST message.

3) A default-ICSI policy is performed, which is a policy that isperformed by the P-CSCF or the S-CSCF and is evaluated when a session isinitiated without an appropriate ICSI. The evaluation may either resultin:

3a) No default ICSI is enforced, see 1) above.

3b) A default ICSI is enforced, see 2) above.

4) When the INITIAL REQUEST comprises an ICSI that is not recognized orsupported, the P-CSCF or the S-CSCF may decide to allow this INITIALREQUEST or the reject the INITIAL REQUEST.

Option 3) may be in the form of an IF . . . ELSE . . . construction. Forinstance:

IF method = INVITE and media = audio THEN default ICSI = multi mediatelephone (option 3b) ELSE no default ICSI (option 3a).

The default-ICSI policy can for example use a similar format/syntax asis used to send the iFC (Initial Filter Criteria) from the HSS to theS-CSCF.

It is proposed that default ICSI information is stored in the P-SCSFand/or S-CSCF after it has been made available by the HSS or isaccessible by the P-SCSF and/or S-CSCF for a particular user that forinstance has registered to the IMS network. The default ICSI informationmay be specific for the user terminal UE who initiated the session or onbehalf of which the session is initiated. This provides a flexiblesystem that can be optimized for each user terminal UE.

Default ICSI Information

As described above, the default ICSI information is stored in or madeaccessible to the P-SCSF and/or S-CSCF to be used in the default ICSIprocedure.

The default ICSI information comprises for each associated user terminalUE information about if a default ICSI is to be enforced or not, and ifso, what ICSI is to be enforced. Furthermore, the default ICSIinformation may comprise a condition that first the default-ICSI policyis to be performed, comprising testing a condition. This lastinformation could be different for each registered user terminal UE ormay be specific for the P-SCSF or S-CSCF handling the INITIAL REQUEST.

Also, the default ICSI information may comprise information how toproceed with the INITIAL REQUEST when the INITIAL REQUEST comprises anICSI that is not supported or recognized by the P-CSCF, S-CSCF or theIMS network. For those cases, the ICSI default information may compriseinformation whether to allow the INITIAL REQUEST or to abort the INITIALREQUEST.

According to an embodiment, the default ICSI information database asmade available to the P-SCSF and/or the S-CSCF may be structured asshown in table 1. Upon registration of a user terminal UE new defaultICSI information may be added to the default ICSI information database.When a registration of a user terminal UE lapses, the correspondingdefault ICSI information may be removed from the default ICSIinformation database.

So, according to an embodiment, the default ICSI procedure comprisestesting at least one parameter in the INITIAL REQUEST and deciding basedon the at least one tested parameter and the default ICSI information toadd a default ICSI to the INITIAL REQUEST, where the default ICSI isspecified by the default ICSI information, or not to add a default ICSIto the INITIAL REQUEST. The parameter may be a combination of:

the type of request, being at least one of INVITE request, MESSAGErequest, REFER requests, SUBSCRIBE request,

the type of media requested, being at least one of audio, video.

TABLE 1 IF ICSI User unrecognized or terminal Default ICSI? Default ICSI= not supported: 1 Yes multi media telephony Abort 2 Yes push to talkAllow 3 No — Abort 4 No — Allow 5 Execute policy If method = INVITE,multi Abort media telephony If else, messaging 6 Execute policy Ifmethod = INVITE and Allow media = audio, multi media telephony If else,No default ICSI

HSS

According to an embodiment, the HSS is a computer as shown in FIGS. 2 aand 2 c, arranged to perform the functionality described.

FIG. 3 schematically depicts a flow diagram as may be performed by theHSS during a registration procedure according to an embodiment. In afirst action 100, the HSS receives a REGISTER message from a userterminal UE. In reaction to the receipt of this REGISTER message, theHSS generates default ICSI information based upon subscriptioninformation stored in memory ME of the HSS. The generated default ICSIinformation is then transmitted to the P-CSCF and/or the S-CSCF inaction 102. The P-CSCF and/or the S-CSCF store this default ICSIinformation for later use.

Of course, it will be understood that the registration procedure itselfmay comprise many more actions, such as authentication and authorizingactions, as will be understood by a skilled person. A detailed exampleof a registration procedure according to the 3GPP specifications (TS23.228 and TS 24.229) is shown in FIG. 5 that will be understood by askilled person. In FIG. 5 the actions that relate to the default ICSIinformation as described here are indicated.

The default ICSI information may be transferred to the S-CSCF as part ofthe user data download over the Cx interface in the registrationprocedure. S-CSCF inserts this data in the final 200 OK of theRegistration procedure. P-CSCF does not forward the information in the200 OK sent to the user terminal.

FIG. 5 depicts a message sequence diagram comprising a number of actionsas may be performed during registering.

In a first action 2 a REGISTER message (2.Register in FIG. 5) istransmitted from the user terminal UE to the P-CSCF. The purpose of thismessage is to register the user's SIP URI with a S-CSCF in the homenetwork.

In a next action 3 a DNS action is performed by the P-CSCF by consultinga DNS database. Based on the user's SIP URI, the P-CSCF determines thatthe user terminal UE is registering from a visiting domain and performsthe DNS queries to locate the I-CSCF in the home network. Whenforwarding the REGISTER the P-CSCF needs to specify the protocol, portnumber and IP address of the I-CSCF server in the home network to whichto send the REGISTER. The P-CSCF tries to find this information byquerying the DNS.

In a next action 4 the REGISTER message is forwarded by the P-CSCF tothe I-CSCF. The P-CSCF needs to be in the path for all mobile originatedand mobile terminated requests for this user. The P-CSCF binds thepublic user identity under registration to the Contact header suppliedby the user.

In a next action 5 the user registration status query is checked by theI-CSCF by consulting the HSS. The I-CSCF requests information related tothe subscriber registration status by sending the private user identity,public user identity and visited domain name to the HSS. The HSS returnsthe S-CSCF required capabilities and the I-CSCF uses this information toselect a suitable S-CSCF.

In a next action 6 the REGISTER message is forwarded by the I-CSCF tothe S-CSCF.

In a next action 7 authentication is executed by the S-CSCF byconsulting the HSS.

In a next action 8 Authentication Vector Selection is performed by theS-CSCF. The S-CSCF selects an authentication vector for use in theauthentication challenge.

In next actions 9, 10 and 11 the S-CSCF sends the authenticationchallenge to the user terminal UE via the I-CSCF and the P-CSCF. TheP-CSCF removes any keys received in the “401 unauthorized response” andforwards the rest of the response to the UE.

In next action 12 upon receiving the “401 unauthorised response”, theuser terminal UE calculates the response, and sends the response in theREGISTER message to the P-CSCF in a next action 13.

In a next action 14 a DNS action is performed by the P-CSCF byconsulting the DNS.

In a next action 15 the REGISTER message is forwarded by the P-CSCF tothe I-CSCF.

In a next action 16 the user registration status query is checked by theI-CSCF consulting the HSS. The HSS returns the S-CSCF name which waspreviously selected in action 5

In a next action 17 the REGISTER message is forwarded by the I-CSCF tothe S-CSCF. Upon receiving an integrity protected REGISTER carrying theauthentication response, S-CSCF checks the response. If the check issuccessful then the user has been authenticated and the public useridentity is registered in the S-CSCF.

In a next action 18 authentication is completed. In response to that,user data is downloaded over the Cx interface from the HSS to the S-CSCFcomprising default ICSI information. Next, the registration is completedby forwarding a “200 OK” message comprising default ICSI informationfrom the S-CSCF to the I-CSCF and the P-CSCF in actions 20, 21. Inaction 22 a “200 OK” message is transmitted from the P-CSCF to the userterminal UE.

It is noted that this flow diagram is not complete.

Originating Case

In the originating case when a user terminal UE initiates a session, theuser terminal UE sends an INITIAL REQUEST message to the P-CSCF whichserves as its outbound proxy.

When the INITIAL REQUEST does not comprise an ICSI or comprises an ICSIthat is not recognized or supported by the IMS network, the default ICSIprocedure is executed by the P-SCSF using the stored default ICSIinformation to decide how to process this INITIAL REQUEST message. Basedon the default ICSI information stored in the P-SCSF or being accessibleby the P-CSCF, that is associated with the particular user terminal UEsending the INITIAL REQUEST, the P-SCSF evaluates if an ICSI is to beadded to the INITIAL REQUEST message or not, and if so, what ICSI shouldbe added to the INITIAL REQUEST message. After the ICSI is added to theINITIAL REQUEST (or not), the INITIAL REQUEST message is furtherprocessed in the same way all INITIAL REQUEST messages are processed,for instance forwarded. So, four options can be identified:

1) No default ICSI is enforced; this means that no ICSI is added by theP-SCSF to the INITIAL REQUEST message on calls originated through it.

2) A default ICSI is enforced; this means that a default ICSI is addedby the P-SCSF to the INITIAL REQUEST message.

3) A default-ICSI policy is performed, which is a policy that isperformed by the P-CSCF or the S-CSCF and is evaluated when the userterminal UE initiates a session without including an appropriate ICSI.The evaluation may either result in:

3a) No default ICSI is enforced, see 1) above.

3b) A default ICSI is enforced, see 2) above.

4) When the INITIAL REQUEST comprises an ICSI that is not recognized orsupported, the P-CSCF may decide to allow this INITIAL REQUEST or thereject the INITIAL REQUEST.

P-CSCF

According to an embodiment, the P-CSCF is a computer as shown in FIGS. 2a and 2 b, arranged to perform the functionality described. FIG. 4schematically depicts a flow diagram as may be performed by the P-CSCFaccording to an embodiment.

In a first action 200, the P-CSCF receives an INITIAL REQUEST messagefrom a user terminal UE. First, in action 201, it is checked if theINITIAL REQUEST comprises an ICSI.

If the INITIAL REQUEST does not comprise an ICSI, in action 202 thedefault ICSI procedure is performed using the default ICSI informationfrom memory ME. In fact, in action 202 it is decided to choose foroption 1), 2) or 3) as described above. Based on the default ICSIinformation a new INITIAL REQUEST+ message is generated in action 203,now possibly comprising an ICSI. Finally, in action 204, the normalINITIAL REQUEST procedure is continued using the new INITIAL REQUEST+message.

If in action 201 it is determined that the INITIAL REQUEST message doescomprise an ICSI, continues with action 205, in which it is checked ifthe ICSI comprised in the INITIAL REQUEST is recognized (or supported)by the P-SCSF. If so, the P-SCSF may continue with action 204. If theICSI is not recognized (or supported), the P-CSCF may continue withaction 206 in which it is decided, based on the default ICSIinformation, to allow the INITIAL REQUEST and continue with action 204,or not to allow the INITIAL REQUEST and abort the set up of the session.

FIG. 6 shows a more default example according to the 3GPP specifications(TS 23.228 and TS 24.229), that will be readily be understood by askilled person. A SIP INVITE is used to illustrate the principle. Thesame principle is applicable also for other SIP methods.

FIG. 6 depicts a message sequence diagram comprising a first action 1 inwhich an INVITE is sent from a user terminal UE#1 to the P-CSCF.

In action 2, a “100 Trying” message is sent back by the P-CSCF to theuser terminal UE#1.

In a next action 3, the P-CSCF forwards the INVITE to the S-CSCF and thedefault ICSI information is added.

In action 4, a “100 Trying” is sent back by the S-CSCF to the P-CSCF.

In a next action 5, evaluation of Initial Filter Criterias is performedby the S-CSCF.

In a next action 6, the INVITE is further forwarded into the network bythe S-CSCF.

In action 7, a “100 Trying” message is received by the S-CSCF.

In an action 8, a “183 Session progress” is received by the S-CSCF whichis forwarded to the P-CSCF in an action 9. After this, QoS resources areauthorized by the P-CSCF.

It is noted that this flow diagram is not complete.

Terminating Case

In the above example (originating case) the default ICSI procedure wasexecuted by the P-SCSF at the home side of the IMS network. According tothis example, an INITIAL REQUEST message arrives in an I-CSCF on theterminating side, where the INITIAL REQUEST does not comprise an ICSI orcomprises an ICSI that is not recognized by the IMS network.

The I-CSCF queries the HSS to find out to which S-CSCF the user terminalUE to which the INITIAL REQUEST is addressed has been allocated. Whenthe INITIAL REQUEST reaches the appropriate S-CSCF, the S-CSCF maydetect that the INITIAL REQUEST does not contain an ICSI or comprises anICSI that is not recognized/supported by the IMS network. The S-CSCFcomprises or has access to default ICSI information and uses thisinformation to perform the default ICSI procedure as described above todecide whether or not to add an ICSI to the INITIAL REQUEST, and if so,to decide what ICSI is added to the INITIAL REQUEST. So, again fouroptions can be identified:

1) No default ICSI is enforced; this means that no ICSI is added to theINITIAL REQUEST message by the S-CSCF on calls originated through it.

2) A default ICSI is enforced; this means that a default ICSI is addedto the INITIAL REQUEST message by the S-CSCF.

3) A default-ICSI policy is performed, which is a policy that isperformed by the S-CSCF and is evaluated when the session is initiatedwithout including an appropriate ICSI. The evaluation may either resultin:

3a) No default ICSI is enforced, see 1) above.

3b) A default ICSI is enforced, see 2) above.

4) When the INITIAL REQUEST comprises an ICSI that is not recognized orsupported, the S-CSCF may decide to allow this INITIAL REQUEST or thereject the INITIAL REQUEST.

AS-Originated Calls

As described above, not all sessions are initiated by user terminals UE.Also application servers AS may initiate sessions, so called applicationserver initiated originated SIP communication. An application server ASmay initiate a session either on behalf of a user terminal UE or as anapplication server independent procedure. The application server doesthis by sending an INITIAL REQUEST to the associated S-CSCF. When theapplication server AS does so on behalf of the user terminal UE, theINITIAL REQUEST is marked with an “ORIG” parameter to instruct theS-CSCF that the originating call behaviour of the associated userterminal UE is to be applied (invocation of originating services, noforking etc). If an INITIAL REQUEST of the application server AS doesnot comprise an ICSI or comprises an ICSI that is not recognized by theIMS network, the S-CSCF may perform a similar functionality as theP-SCSF when receiving an INITIAL REQUEST with no valid ICSI. DefaultICSI information is provided to the S-CSCF, based on which the S-CSCFcan perform the default ICSI procedure to decide how to process anINITIAL REQUEST not comprising valid ICSI. Again, four options can beidentified:

1) No default ICSI is enforced; this means that no ICSI is added to theINITIAL REQUEST message by the S-CSCF on calls originated through it.

2) A default ICSI is enforced; this means that a default ICSI is addedto the INITIAL REQUEST message by the S-CSCF.

3) A default-ICSI policy is performed, which is a policy that isperformed by the S-CSCF and is evaluated when the session is initiatedwithout including an appropriate ICSI. The evaluation may either resultin:

3a) No default ICSI is enforced, see 1) above.

3b) A default ICSI is enforced, see 2) above.

4) When the INITIAL REQUEST comprises an ICSI that is not recognized orsupported, the S-CSCF may decide to allow this INITIAL REQUEST or thereject the INITIAL REQUEST.

So, for calls originated by the application server AS on behalf of theuser terminal UE, the S-CSCF can apply the same principles as describedfor the terminating case above: the S-CSCF acts as the enforcement pointin the termination case and the cases where a session isinitiated/originated by an application server AS, where the P-CSCF isthe enforcement point for the originating case initiated by the userterminal UE.

When the INITIAL REQUEST does not comprise an ICSI and the storeddefault ICSI information evaluates to “insert ICSI value”, the S-CSCFexecutes the default ICSI procedure, adds the appropriate ICSI to theINITIAL REQUEST. After the ICSI is added to the INITIAL REQUEST (ornot), the INITIAL REQUEST message is further processed in the same wayall INITIAL REQUEST messages are processed, for instance forwarded.

FIG. 8 provides a general flow diagram according to an embodiment. FIG.8 shows a flow diagram as may be performed by a control entity CE, suchas a P-CSCF, a S-CSCF or a P-CSCF and a S-CSCF. According to FIG. 8, thecontrol entity performs:

receiving a request for setting up a session in the communicationsnetwork in action 301,

determining if the request comprises a valid Communication ServiceIdentifier (CSI), the Communication Service Identifier identifying thetype of communication service of the session that is to be establishedover the communications network in action 302, and if the request doesnot comprise a valid Communication Service Identifier, performing action303:

executing a default CSI procedure using default CSI information.

So, based on the above it will be understood that the default ICSIinformation is provided or made accessible to the P-SCSF and the S-CSCFduring registration, and the S-CSCF acts as the enforcement point in thetermination case and the case wherein a session is initiated by theapplication server AS, where the P-CSCF is the enforcement point for theoriginating case initiated by the user terminal UE.

S-CSCF (for Terminating Option and AS Option):

According to an embodiment, the S-CSCF is a computer as shown in FIGS. 2a and 2 b, arranged to perform the functionality described.

The actions as may be performed by the S-CSCF are in fact similar to theactions as may be performed by the P-CSC as already described above withreference to FIG. 4.

FIG. 7 shows in more detail an example of a terminating case accordingto the 3GPP specifications (TS 23.228 and TS 24.229), which will beunderstood by a skilled person. The SIP Invite is used to illustrate theprinciple. As mentioned above, the same principle is applicable also forother SIP requests.

FIG. 7 depicts a message sequence diagram comprising a first action 1 inwhich an INVITE from an I-CSCF is received by the S-CSCF.

In action 2, a “100 Trying” message is sent back by the S-CSCF. In thisaction the default ICSI information may be evaluated, for instance, thedefault ICSI policy may be executed.

In action 3, Initial Filter Criterias are evaluated by the S-CSCF.

In action 4 the INVITE is forwarded by the S-CSCF to the P-CSCF and inaction 5, a “100 Trying” message is sent back by the P-CSCF to theS-CSCF.

In action 6 the INVITE is forwarded by the P-CSCF to a user terminalUE#2 and in action 7, a “100 Trying” message is sent back by the userterminal UE#2 to the P-CSCF.

In action 8, the user terminal UE2# sends a “183 Session Progress” tothe P-CSCF.

In action 9, the QoS resources are authorized by the P-CSCF.

In action 10, the “183 Session Progress” is forwarded by the P-CSCF tothe S-CSCF.

It is noted that this flow diagram is not complete.

For AS originated calls that are not established on a user's behalf, theS-CSCF can use a node global value, typically provisioned to the S-CSCFas part of exchange data. The S-CSCF that receives an AS originated callthat is not on behalf of a user terminal UE, could include a defaultICSI that is not particular for the respective user terminal UE but is anode global value, i.e. is a default ICSI stored on the S-CSCF for allAS originated calls that are not on behalf of a user terminal UE.

Further Remarks

As mentioned above, the term INITIAL REQUEST is used to refer to anyrequest that is used to set up a session and may not necessarily be theactual first request exchanged. The INITIAL REQUEST to set up a sessionmay in fact be divided in more than one message transmitted through theIMS network.

As described above, the INITIAL REQUEST may comprise a valid ICSI,meaning comprising an ICSI that is recognized and supported. If no ICSIis comprises or an ICSI is comprised that is not recognized orsupported, the ICSI is referred to as non valid.

The P-CSCF and the S-CSCF are here described as separate modules.However, it will be understood that the P-CSCF and the S-CSCF may beformed as one module, for instance formed as one computer, integratingthe functionality of both the P-CSCF and the S-CSCF.

The P-CSCF, S-CSCF and the HSS as here described may be formed ascomputers. Such computers may comprise or have access to memorycomprising instructions that are readable and executable by theprocessor unit PU to enable the computer 10 to perform the embodimentsdescribed.

According to an embodiment there is provided a computer program that,when loaded on a computer, provides the computer with the functionalityto perform one of the methods described here. According to a furtherembodiment, there is provided a data carrier, comprising such a computerprogram. The data carrier may be a memory, a floppy, a CD, DVD etc.

The embodiments above relate to an IMS network, but it will beunderstood that that the embodiments may also be put to practice inother networks, generally referred to as communications networks, like aGSM, Code Division Multiple Access (CDMA), Time Division Multiple Access(TDMA), Universal Mobile Telecommunication System (UMTS), or 4G network.

Also, the P-CSCF and the S-CSCF are examples of entities in which theembodiments may be employed. Of course, it will be understood that theembodiments may be put to practice in similar other entities playingsimilar roles. These entities may be referred to as control entities,for instance being a S-CSCF or a P-CSCF.

Also, the embodiments refer to a home subscriber server (HSS). However,it will be understood that this may more generally be referred to as asubscriber database, for instance being a home subscriber server (HSS).

The embodiments above describe an IMS Communication Service Identifier,but it will be understood that in general, the embodiments relate to anyCommunication Service Identifier, for instance being an IMSCommunication Service Identifier. Accordingly, a default CSI proceduremay be provided, for instance being the default ICSI procedure describedabove, where the default CSI procedure uses default CSI information, forinstance being default ICSI information.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1-24. (canceled)
 25. A Control Entity for setting up a session in acommunications network, comprising an input device for receiving arequest to set up a session in the communications network; a processorunit for processing the request; and an output device for sendingmessages; wherein the Control Entity further comprises or has access toa memory for storing information, and wherein the processor unit isarranged to: determine if the request comprises a valid CommunicationService Identifier (CSI), the CSI identifying the type of communicationservice of the session that is to be established over the communicationsnetwork; and if the request does not comprise a valid CSI, the processorunit is arranged to execute a default CSI procedure using default CSIinformation stored in the memory, said default CSI information beingbased upon subscription information, and, for carrying out said defaultCSI procedure, said processor unit configured to: add a default CSI tothe request, in case the request does not comprise a CSI, where thedefault CSI is specified by the default CSI information; or test atleast one parameter in the request and decide based on the at least onetested parameter and the default CSI information to add a default CSI tothe request, where the default CSI is specified by the default CSIinformation, or not to add a default CSI to the request.
 26. The ControlEntity of claim 25, where the at least one parameter may be acombination of the type of request and the type of media, and, where incase the communications network is an IP Multimedia Subsystem network,the type of request may be one of INVITE request, MESSAGE request, REFERrequests, SUBSCRIBE request, and the type of media may be one of audio,video.
 27. The Control Entity of claim 25, where, in case the requestcomprises a CSI that is not recognized or supported by the controlentity or the communications network, the default CSI procedure decidesto allow or abort the request based on the default CSI information. 28.The Control Entity of claim 25, where the Control Entity is a Proxy CallSession Control Function that is arranged to act as a first point ofcontact within the communications network for a user terminal, and isarranged to receive a request from a user terminal for setting up asession in the communications network with a remote user terminal. 29.The Control Entity of claim 28, where the default CSI information isspecific for the user terminal the request is received from.
 30. TheControl Entity of claim 25, where the Control Entity is a Serving CallSession Control Function that in use is arranged to provide services,and is arranged to receive a request from an application server forsetting up a session in the communications network.
 31. The ControlEntity of claim 30, where the default CSI information is specific forthe user terminal on behalf of which the request is made by theapplication server.
 32. The Control Entity of claim 25, where thecontrol entity is a Proxy Call Session Control Function and a ServingCall Session Control Function.
 33. A method in a Control Entity in acommunications network for setting up a session in a communicationsnetwork, the method comprising: receiving a request for setting up asession in the communications network; determining if the requestcomprises a valid Communication Service Identifier (CSI), the CSIidentifying the type of communication service of the session that is tobe established over the communications network; and if the request doesnot comprise a valid CSI, executing a default CSI procedure usingdefault CSI information, said default CSI information being based uponsubscription information, said default CSI procedure comprising: addinga default CSI to the request, in case the request does not comprise aCSI, where the default CSI is specified by the default CSI information,or testing at least one parameter in the request and deciding based onthe at least one tested parameter and the default CSI information to adda default CSI to the request, where the default CSI is specified by thedefault CSI information, or not to add a default CSI to the request. 34.The method of claim 33, where the at least one parameter may be acombination of the type of request and the type of media, and, in casethe communications network is an IP Multimedia Subsystem network, thetype of request may be one of INVITE request, MESSAGE request, REFERrequests, SUBSCRIBE request, and the type of media may be one of audio,video.
 35. The method of claim 33, where, in case the request comprisesa CSI that is not recognized or supported by the control entity or thecommunications network, the default CSI procedure decides to allow orabort the request based on the default CSI information.
 36. The methodof claim 33, where the request is a request from a user terminal forsetting up a session in the communications network with a remote userterminal.
 37. The method of claim 36, where the default CSI informationis specific for the user terminal the request is received from.
 38. Themethod of claim 33, where the request is a request from an applicationserver for setting up a session in the communications network.
 39. Themethod of claim 38, where the default CSI information is specific forthe user terminal on behalf of which the request is made by theapplication server.
 40. A subscriber database configured to be part of acommunications network, comprising: an input device for receiving aregister message from a user terminal; a processor unit for processingthe register message; and an output device; the subscriber databasefurther comprising or having access to a memory for storing subscriptioninformation, and wherein the subscriber database is configured to:generate default CSI information based upon subscription informationstored in the memory, in reaction to the receipt of the registermessage; and transmit the generated default CSI information to at leastone control entity in the communications network via the output device.41. The subscriber database of claim 40, wherein the default CSIinformation is specific for the user terminal the register message isreceived from.
 42. The subscriber database of claim 40, where thesubscriber database is arranged to work in an IP Multimedia Subsystemnetwork and the subscriber database is a home subscriber server.
 43. Amethod for registering a user terminal in a communications network,wherein a subscriber database performs the steps of: receiving aregister message from a user terminal; generating default CSIinformation based upon subscription information in reaction to thereceipt of the register message; and transmitting the generated defaultCSI information to at least one Control Entity in the communicationsnetwork.
 44. The method of claim 43, wherein the default CSI informationis specific for the user terminal the register message is received from.45. An IP Multimedia Subsystem network, comprising a Control Entity forsetting up a session in a communications network and a subscriber entityconfigured to be part of the communications network; and wherein saidControl Entity comprises: an input device for receiving a request to setup a session in the communications network; a processor unit forprocessing the request; and an output device for sending messages;wherein the Control Entity further comprises or has access to a memoryfor storing information, and wherein the processor unit is arranged to:determine if the request comprises a valid Communication ServiceIdentifier (CSI), the CSI identifying the type of communication serviceof the session that is to be established over the communicationsnetwork; and if the request does not comprise a valid CSI, the processorunit is arranged to execute a default CSI procedure using default CSIinformation stored in the memory, said default CSI information beingbased upon subscription information, and, for carrying out said defaultCSI procedure, said processor unit configured to: add a default CSI tothe request, in case the request does not comprise a CSI, where thedefault CSI is specified by the default CSI information; or test atleast one parameter in the request and decide based on the at least onetested parameter and the default CSI information to add a default CSI tothe request, where the default CSI is specified by the default CSIinformation, or not to add a default CSI to the request; and whereinsaid subscriber database comprises: an input device for receiving aregister message from a user terminal; a processor unit for processingthe register message; and an output device; the subscriber databasefurther comprising or having access to a memory for storing subscriptioninformation, and wherein the subscriber database is configured to:generate default CSI information based upon subscription informationstored in the memory, in reaction to the receipt of the registermessage; and transmit the generated default CSI information to at leastone control entity in the communications network via the output device.46. The IP Multimedia Subsystem network of claim 45, where the ControlEntity is one of: a Proxy Call Session Control Function that is arrangedto act as a first point of contact within the communications network fora user terminal, and is arranged to receive a request from a userterminal for setting up a session in the communications network with aremote user terminal; or a Serving Call Session Control Function that inuse is arranged to provide services, and is arranged to receive arequest from an application server for setting up a session in thecommunications network.